The company said it partnered with NebuAD to build behavioral profiles of users and sell them to third-party advertising networks to serve more tailored ads.
Ted Schremp, vice president of Charter Communications, told Wired.com the system initially will be tested with subscribers in Ft. Worth, Texas; San Luis Obispo, Calif.; Oxford, Mass.; and Newton, Conn.
Charter said customers would be able to opt out of the service, but the opt-out operation must be done on every home computer and redone if cookies on the computer are deleted. Opting out of the service would only stop targeted ads, not tracking of Web surfing.
Other Internet service providers, including WOW, Embarq, CenturyTel and Broadstripe, have employed similar systems.
Charter said it will start testing the system within 30 days and will decide whether to roll it out to its other customers a few months after that.
"The advertising you typically see online will better reflect the interests you express through your Web-surfing activity," Charter wrote in letters sent to customers in the initial cities. "You will not see more ads - just ads that are more relevant to you."
"All we are doing is, in an anonymous format, providing additional context to serve those ads," Schremp told The New York Times. "To the extent those ads are more meaningful to me as Ted Schremp, I will have a better Internet experience than the generic ads that are part of Yahoo and everything online."